Redditors as a group tend to lynch posters who don't use Imgur to host.

So though it's not official, Imgur has a near-monopoly on images shared with Reddit.

Why? It's a good story...

Redditors are completely focused on discussing links to online content. Anyone can submit these links, which others can then vote up or down or post comments on. Upvoting is similar to the "like" button on Facebook, except sharing is not limited just to your own social circles. The more upvotes a link gets, the higher that link appears on the site and the more visitors the linked site will get from all site visitors. To get a high ranking these upvotes also need to accumulate within a short time span, since old links gradually drop lower on the page. A popular link can push thousands of visitors to the linked site.

Often called a social news site, the site is now as much about posting interesting or funny pictures as it is about news. If you look at the Reddit main page, chances are that half of the links lead to Imgur. Imagine the traffic gained by having half of the links on the main page of one of the most popular sites on the Internet pointing to you. How did this happen? In an interview last year, Imgur founder Alan Schaaf said "the Reddit community decided they liked imgur because it’s simple, easy, and hassle free, but they gave it a chance because it was made by a redditor for other redditors".

To understand how this really happened, we need to imagine what the state of Reddit was before Imgur made its appearance. Back then posting links to images was becoming increasingly popular, but there was discontent with the available image hosting sites. Since Reddit only allows links and comments, posting images on the site required hosting them elsewhere. Image links to other image hosting sites would often not work or the sites would be slow or could not cope with the bandwidth required to support the deluge of visits a successful Reddit post can bring.

Imgur not only solved the reliability issues, but also made it easier to upload pictures by not requiring that users have an account on the site. Images could even be linked to directly without having to look at annoying banner advertising, even that meant loss of ad revenue for Imgur. These are all good reasons for the popularity of the site, but it was just as important that redditors felt that it was made for them. The site was launched via a Reddit post, in which the founder put himself out there and was openly discussing these issues with redditors and engaging with them on a human level.

Because of the trust gained through his openness, Imgur has become immensely popular. If there are no ads around the images, how then is Imgur now supporting its huge bandwidth costs? The answer is that many people now have such positive feelings towards Imgur that they are voluntarily linking to advertising-supported image pages on the site instead of using direct image links. This shows how important it can be to be genuine. The success of Imgur is not only in its convincing feature set, but in that the founder showed himself to be the kind of character that made his audience grateful and made him want him to succeed in return.

Good story, except that Imgur does not have huge bandwidth costs.

They're using Cloudflare as a CDN, which gets them unlimited bandwidth for a low monthly price.

The main reason Imgur has a near-monopoly on Reddit is that Redditors actively campaign against non-Imgur links.

An example is here, where the Redditor chastises a n00b for linking to Instagram instead of uploading the picture to Imgur first and then linking to Imgur:

http://www.reddit.com/r/Laina/comments/1m22xw/breaking_bad_pretty_epic/

As a result of many Redditors doing this, Imgur takes images and traffic away from other sites.

It is an insidious and brilliant strategy that has made Imgur one of the top 100 sites in the world.

The way they process images and then immediately have them available by adding a .png, .jpg, .gif to the end of the url is pretty smart and super useful when trying to quickly share an image.

Yes! It is surprising there is no other service on the Internet that offers this service.

Reddit ask me anything with the founder of Imgur:

http://www.reddit.com/r/reddit.com/comments/7zlyd/my_gift_to_reddit_i_created_an_image_hosting/